UCLA

A hydrogel can be viewed as a unique combination of liquid and solid, the liquid side properties endow it with generally good biocompatibility and high porosity for fast diffusion, yet they are shape fixable as a solid material, by applying knowledge of molecular and structural engineering, they can also be made to bear moderate external loads. These unique combinations of physical and chemical properties make them promising materials for various applications.

However, fragileness and low durability are major obstacles that hindered broad application of hydrogels in practice. We developed a class of strong and tough hydrogels by tailoring hydrogel structure across several hierarchical length-scales via modulation of polymer aggregation. The series of hydrogels were prepared by combining freeze-casting and salting out in sequential steps, which could realize simultaneously high strength, toughness, stretchability and fatigue resistance.

In Chapter 1, the fundamentals and fracture mechanics of hydrogel were discussion. The design principals for improving hydrogel mechanical properties include extending chain length, increasing chain fracture energy, promoting stress distribution and adopting anisotropic design.

In Chapter 2 and 3, the mechanism of preparing tough hydrogels via freeze-casting and salting out step was discussed and hydrogels with simultaneous high toughness, fatigue resistance was realized.

In Chapter 4 and 5, utilizing the developed tough hydrogel, the applications of hydrogel reinforcement coating and 3D printing were explored. These applications show that the developed tough hydrogels have significant versatility for various applications.